1. Field of the Invention
This invention relates to a drive unit for initialization, especially to a drive unit for initialization to reset a condition of step-out of a stepping motor for driving a pointer mounted in an indicator of a vehicle.
2. Description of the Related Art
An indicator shown in FIG. 1 exists usually as an indicator for a vehicle by a stepping motor. In FIG. 1, the indicator includes a stepping motor 1, a pointer 2 interlocking rotation of the stepping motor 1 and a drive unit 8 for stepping motor (call a drive unit 8 simply hereafter) for rotating normally and reversely the stepping motor 1. The stepping motor 1, as mentioned above, includes two exciting coils 1a1 and 1a2, a rotor 1b being magnetized each three poles alternately N pole and S pole and rotating to follow the change of excited conditions of the exciting coils 1a1 and 1a2, and a gear 1d transmitting a driving force of the rotor 1b to the pointer 2.
The stepping motor 1, which is mounted on the back side against the gear id at the same side of the pointer 2, includes a piece 1e as a driven member interlocking rotation of the rotor 1b; a not-shown receiving case for receiving the exciting coils 1a1 and 1a2, the rotor 1b, the gear 1d and the piece 1e; and a stopper 1f being mounted at the receiving case and stopping mechanically rotation of the rotor 1b to abut on the piece 1e. 
Reverse rotation is defined by rotating the stepping motor 1 to move the piece 1e toward the stopper 1f. A direction of reverse rotation Y 1 is defined by a direction of rotation of the pointer 2 in reverse rotation. Oppositely, normal rotation is defined by rotating the stepping motor 1 to move the piece le apart from the stopper 1f and a direction of normal rotation Y 2 is defined by a direction of rotation of the pointer 2 in normal rotation. The stopper 1f is located to make the pointer 2 point a scale reading of 0 Km/h on a scale plate when the stopper if abuts on the piece 1e. 
When above indicator is used for a car speedometer, the drive unit 8 rotates the rotor 1b correspondingly to an amount of moving xc3xa8-xc3xa8xe2x80x2 of a difference of a target position xc3xa8 and a current position xc3xa8xe2x80x2 of the pointer 2 to make the pointer 2 move the difference of xc3xa8-xc3xa8xe2x80x2 for pointing the target position xc3xa8. The target position xc3xa8 is renewed by an angle datum xc3xa8i whenever the angle datum xc3xa8i calculated with a speed datum by an output of a car speed sensor is inputted. The angle datum xc3xa8i is calculated as reference angle zero degree at speed datum of zero Km/h and increased in proportion of increasing speed datum.
The indicator may have step-out, which is an phenomenon of difference of a required moving amount (difference of xc3xa8-xc3xa8xe2x80x2) and an actual moving amount of the pointer 2, caused by vibration of a car or inputting of an angle datum with superposed noise. If the step-out is repeated, a speed pointed by the pointer 2 is different from a speed datum measured by the speed sensor so that the indicator cannot indicate accurately.
Therefore, for solving such trouble, a later-described initializing operation is acted by the drive unit 8. In the initializing operation, the drive unit 8 rotates reversely the stepping motor 1 to move the piece 1e toward the stopper 1f whenever an ignition switch is turned ON. Thereafter, the drive unit 8 stops electrically rotation of the stepping motor 1 to maintain exciting coils 1a1 and 1a2 in a predetermined initial excited condition when the piece 1e abuts on the stopper 1f and the pointer 2 stops mechanically at an abutting position as a scale reading of 0 Km/h on a scale plate. By acting the initializing operation as mentioned above, when the current position xc3xa8xe2x80x2 is sensed as 0 degree, the pointer 2 points at a scale reading of 0 Km/h as the abutting position. Thus, difference of the speed pointed by the pointer 2 and the speed datum measured by the speed sensor can be reset.
Objects to be Solved
The indicator as mentioned above is initialized at timing when the ignition switch is turned ON. Therefore, the usual indicator cannot indicate a measured value immediately after being activated correspondingly to turning the ignition switch ON. Especially, when the indicator is used for a tachometer, the indicator may not indicate a rotation speed of an engine for an initializing operation although the engine has started. It has been required that motion of the pointer in the initializing operation is hidden from a driver.
To solve such problems, it is considered that the initializing operation is acted at timing when the ignition switch is turned OFF. If time from the initializing operation to starting the indicator is required much, a car is vibrated during the time so that possibility of step-out is increased. Therefore, step-out may be occurred when starting the indicator and then the indicator cannot indicate accurately.
To overcome the above drawback of prior art, one object of this invention is to provide a drive unit for initialization, in which a pointer in an indicator for a vehicle can point immediately after an ignition switch is turned ON by starting the initializing operation correspondingly to an open/close operation of a door of a vehicle, and frequency of seeing motion of a pointer in the initializing operation by a car driver is reduced.
How to Attain the Object
In order to attain the objects, a drive unit for initialization according to this invention, which includes, as shown in FIG. 1 of a basic structure block diagram; drive means 8a-1 for initializing a stepping motor 1 to rotate for actuating a pointer mounted in an indicator of a vehicle so as to move a driven member, interlockingly with rotation of the stepping motor, toward a stopper for stopping the rotation of the stepping motor mechanically by abutting on the driven member; and drive-stop means 8a-2 for stopping the rotation of the stepping motor electrically after the driven member being abutted on the stopper, comprises sensing means 8a-3 for sensing an open/close operation of a door of the vehicle, and drive-start means 8a-4 for starting rotation of the stepping motor by the drive means for initialization correspondingly to an output of the sensing means when an ignition switch is in a state of OFF condition.
According to the above structure, the sensing means senses an open/close operation of a door of a vehicle. The drive-start means starts rotation of the stepping motor by the drive means for initialization correspondingly to an output of the sensing means when the ignition switch is in a state of OFF condition. The drive means for initialization rotates the stepping motor so as to move a driven member, interlockingly with rotation of the stepping motor for actuating a pointer in an indicator of a vehicle, toward a stopper for stopping the rotation of the stepping motor mechanically by abutting on the driven member. The drive-stop means stops the rotation of the stepping motor electrically after the driven member being abutted on the stopper.
A car driver turns the ignition switch ON to start the indicator for a vehicle usually after open and close a door to go into a car. Therefore, the initializing operation can be completed before the ignition switch is turned ON, by starting the operation by the drive means for initialization when the ignition switch is in a state of OFF condition and an open/close operation of a door is sensed.
Advantageously, the drive unit for initialization according to this invention, shown in FIG. 1 of a basic structure block diagram, is characterized by the fact that the sensing means senses an open/close operation of the door of the vehicle when a door-lock switch SW2 is turned ON or OFF to lock or unlock the door in the drive unit for initialization mentioned above.
According to the above structure, when the door-lock switch is turned ON or OFF to lock or unlock the door, the sensing means senses an open/close operation of a door. Therefore, a door-lock switch turning ON or OFF for locking or unlocking a door can be shared for sensing an open/close operation of a door.
Advantageously, the drive unit for initialization according to this invention, is characterized by the fact that the sensing means senses an open/close operation of the door when a courtesy switch is turned ON or OFF to switch a courtesy lamp ON or OFF correspondingly to open or close of the door in the drive unit for initialization mentioned above.
According to the above structure, when the courtesy switch is turned ON or OFF to switch the courtesy lamp ON or OFF correspondingly to open or close of the door, the sensing means senses an open/close operation of a door. Therefore, a courtesy switch turning ON or OFF for switching the courtesy lamp ON or OFF can be shared for sensing an open/close operation of a door.
Advantageously, the drive unit for initialization according to this invention, as shown in FIG. 1 of a basic structure block diagram, is characterized by the fact that the drive-stop means maintains exciting coils of the stepping motor in a predetermined excited condition until the ignition switch SW1 is turned ON to stop electrically the rotation of the stepping motor in the drive unit for initialization mentioned above.
According to the above structure, the drive-stop means maintains exciting coils of the stepping motor in a predetermined excited condition until the ignition switch SW1 is turned ON to stop electrically the rotation of the stepping motor. Therefore, even if the vehicle is vibrated until the ignition switch is turned ON, the pointer has no chance of step-out.
Advantageously, the drive unit for initialization is characterized by the fact that the drive-stop means maintains the exciting coils in a predetermined excited condition and stops the excitation of the exciting coils when the ignition switch is not turned ON after elapsing a predetermined time in the drive unit for initialization mentioned above.
According to the above structure, the drive-stop means stops the excitation of exciting coils when the ignition switch is not turned ON after elapsing a predetermined time for maintaining the exciting coils in the excitation. Therefore, when the ignition switch is not turned ON after elapsing a predetermined time from an open/close operation of the door, the excitation of the exciting coils is stopped so that the excitation of the exciting coils is not maintained for a long while an engine is not started and an alternator does not generate electricity.
Advantageously, the drive unit for initialization according to this invention, is characterized by the fact that the drive-start means starts rotation of the stepping motor by the drive means for initialization when the ignition switch is turned ON in the condition that excitation of the exciting coils is stopped by the drive-stop means in the drive unit for initialization mentioned above.
According to the above structure, the drive-start means starts rotation of the stepping motor by the drive means for initialization when the ignition switch is turned ON in the condition that excitation of the exciting coils is stopped by the drive-stop means. Therefore, when the ignition switch is turned ON in the condition that excitation of the exciting coils is stopped, the initializing operation is acted again so that the indicator is not driven in a condition of stopped excitation of the exciting coils, i.e. in a condition of step-out.
The above and other objects and features of this invention will become more apparent from the following description taken in conjunction with the accompanying drawings.